1. Field of the Invention
The present invention relates to a fluorescent lamp lighting apparatus for lighting up a fluorescent light emitting tube using an electronic lighting circuit.
2. Description of the Related Art
In recent years, as energy savings have become more and more important, an increasing number of fluorescent lamp light apparatuses have adopted a high frequency inverter type electronic lighting circuit, instead of a copper-iron stabilizer as conventionally used. Specifically for a light bulb type fluorescent lamp built in the lighting apparatus as an energy-saving light source replacing a light bulb, the use of this type of electronic lighting circuits is becoming more common in order to realize a lamp having a higher lamp efficiency or light emission efficiency and less weight.
In order to improve the lamp efficiency of the electronic lighting circuit for a light bulb type fluorescent lamp, there has been an attempt to improve the circuit conversion efficiency of the electronic lighting circuit. As a result, the circuit conversion efficiency which was about 80% has been increased to a maximum of about 92%. This has been realized by introducing a series inverter circuit system in an electronic light circuit or by using a MOS field emission power transistor as an electronic component. The value of about 92% is almost the maximum possible value for a circuit conversion efficiency. In order to further improve the lamp efficiency, a different new technique, for example, a technique for reducing a power loss caused by heat generation in an electrode filament coil in the fluorescent light emitting tube is demanded.
FIG. 4 is a diagram illustrating a basic structure of a conventional high frequency inverter type electronic lighting circuit 19 (hereinafter, referred to simply as the xe2x80x9celectronic lighting circuit 19xe2x80x9d). The electronic lighting circuit 19 includes an Inverter circuit section 25 which is driven by a commercial power supply 13. The inverter circuit section 25 lights up a fluorescent light emitting tube 20.
The fluorescent light emitting tube 20 includes a pair of electrode filament coils 21 and 22. The electrode filament coils 21 includes terminals 21a and 21b, and the electrode filament coils 22 includes terminals 22a and 22b. The terminals 21a and 22a are closet than the terminals 22b and 22b to the power supply 13 for applying an electric current to the fluorescent light emitting tube 20.
The terminal 22a of the electrode filament coil 22 is directly connected to the inverter circuit section 25. The terminal 21b of the electrode filament coil 21 is connected to the inverter circuit section 25 via an inductor 24 provided for electric current control. The inductor 24 is connected in series to the terminal 21a. The terminals 21b and 22b of the electrode filament coils 21 and 22 are connected to each other via a capacitor 23. The capacitor 23 and the inductor 24 are included in a resonating circuit. In FIG. 4, an inductance of the inductor 24 is represented by xe2x80x9cLxe2x80x9d, and a capacitance of the capacitor 23 is represented by xe2x80x9cCsxe2x80x9d.
The conventional electronic lighting circuit 19 performs an operation for starting and thus placing a fluorescent lamp into a constant lighting state, using a hot cathode starting system. This will be described below.
Before starting the lamp, the inverter circuit section 25 causes an electric current to flow to the electrode filament coils 21 and 22 of the fluorescent light emitting tube 20 through the capacitor 23 in order to pre-heat the electrode filament coils 21 and 22 and thus cause the electrode filament coils 21 and 22 to emit a sufficient amount of thermoelectric. The capacitor 23 is connected parallel to the fluorescent light emitting tube 20.
When the pre-heating electric current is flown to the electrode filament coils 21 and 22, a starting voltage is applied between the electrode filament coils 21 and 22 within about 1 second, and thus the fluorescent light emitting tube 20 is started. The starting voltage corresponds to a resonating voltage of the resonating circuit including the capacitor 23 and the inductor 24.
The fluorescent light emitting tube 20, after being started, goes into a constant lighting state. In this state, the electric current still flows to the electrode filament coils 21 and 22 via the capacitor 23, and thus heat is generated in the electrode filament coils 21 and 22.
As described above, the conventional electronic lighting circuit 19 realizes the constant lighting state of the fluorescent light emitting tube 20 after pre-heating the electrode filament coils 21 and 22 and then starting the fluorescent light emitting tube 20. After the fluorescent light emitting tube 20 goes into the constant lighting state, the electric current is basically unnecessary. However, since an electric current is required in order to pre-heat the electrode filament coils 21 and 22 by the conventional method using the capacitor 23, the electric current inevitably flows even after the fluorescent light emitting tube 20 goes into the constant lighting state and thus generates heat in the electrode filament coils 21 and 22. This heat generation causes a power loss.
In a currently-used light bulb type fluorescent lamp (for example, a 14 W or 25 W light bulb) which has a luminous flux corresponding to that of a general 60 W or 100 W light bulb, the power loss caused by the heat generation is 0.4 W to 0.5 W per electrode filament coil. In the fluorescent light emitting tube 20, the power loss caused by the heat generation is 0.8 W to 1.0 W per electrode filament coil. These values are not negligible.
FIGS. 5A through 5C show known electronic light circuits used for reducing such a power loss caused by the heat generation In an electrode filament coil during a constant light state of the fluorescent light emitting tube 20. Like elements as those in FIG. 4 bear identical reference numerals.
An electronic light circuit 19a shown in FIG. 5A adopts a so-called cold cathode starting system. The electrode filament coils 21 and 22 of the fluorescent light emitting tube 20 are respectively shortcircuited by leads 26 and 27. The leads 26 and 27 are respectively connected parallel to the electrode filament coils 21 and 22. The fluorescent light emitting tube 20 is started in a cold cathode state with no thermoelectrons being emitted. Due to such a structure, the power lose caused by the heat generation in the electrode filament coils 21 and 22 is reduced.
An electronic lighting circuit 19b shown in FIG. 5B is disclosed in Japanese Laid-Open Publication No. 10-199686. Diodes 28 and 29 are respectively connected parallel to the electrode filament coils 21 and 22 of the fluorescent light emitting tube 20. Due to such a structure, the amount of the electric current flowing to each of the electrode filament coils 21 and 22 is reduced to half. Thus, the power loss caused by the heat generation is also reduced to about half.
An electronic lighting circuit 19c shown in FIG. 5C is disclosed in Japanese Laid-Open Publication No. 5-13186. Capacitors 31 and 32 are respectively connected parallel to the electrode filament coils 21 and 22 of the fluorescent light emitting tube 20., The capacitor 31 branches the electric current into the capacitor 31 and the electrode filament coil 21, and the capacitor 32 branches the electric current into the capacitor 32 and the electrode filament coil 22. Due to such a structure also, the amount of the electric current flowing to each of the electrode filament coils 21 and 22 is reduced. Thus, the power loss caused by the heat generation is also reduced.
Fluorescent lamps are now expected to be used in houses which is one important field of use of light bulbs, in addition to department stores, restaurants, hotels and other business settings in which the fluorescent lamps are mainly used conventionally. Generally in fluorescent lamps, an electron radiating substance filling the electrode filament coils at the time of starting the lamp easily scatters. Accordingly, it is known that as the number of times the fluorescent lamp is lit on or off is increased, the life of the lamp is shortened. This is also true with light bulb type fluorescent lamps. Lamps which are used in houses are inevitably lit on or off a greater number of times than lamps used in business settings. It is demanded to increase the number of times the lamp can be lit on and off until the life of the lamp ends (hereinafter, the number of times the lamp cam be lit on and off until the life of the lamp ends will be referred to as the xe2x80x9clamp life light on/off characteristicxe2x80x9d).
The lamp life lighting on/off characteristic is conventionally about 5000 times. Now, the lamp life lighting on/off characteristic is demanded to be increased to be 4 times larger, i.e., a t least 20000 times. According to an experiment performed by the prevent inventors, the average life of the conventional lamp was 6000 hours. This corresponds to an average life obtained in a test by which the lamp is kept on for 2.5 hours and then kept off for 0.5 hours.
In order to respond to. this demand, Japanese Laid-Open Publication No. 62-126596 discloses an electronic lighting circuit 40 shown in FIG. 6. A temperature positive characteristic resistance element (positive character thermistor or PCT) 33 Is connected parallel to the capacitor 23 so as to be opposite to the commercial power supply 13 with respect to the fluorescent light emitting tube 20. Due to such a. structure, a large amount of pre-heating electric current flows to the electrode filament coils 21 and 22 via the temperature positive characteristic resistance element 33 before the fluorescent light emitting tube 20 is started. Thus, the lamp life lighting on/off characteristic is improved.
The present inventors performed studies on a fluorescent lamp using an electronic lighting circuit, especially a light bulb type fluorescent lamp having a built-in electronic lighting circuit, In order to realize both reduction in a power loss caused by the heat generation in an electrode filament coil in the constant lighting state of the lamp and increase in the lamp life lighting on/off characteristic. As a result, the present inventors found that the electronic lighting circuits shown in FIGS. 5A through 5C have an undesirable possibility that the lamp life lighting on/off characteristic is not increased.
In the cold cathode starting system shown in FIG. 5A with no emission of thermoelectrons, the power loss caused by the heat generation in the coils can sufficiently be reduced. However, the voltage for starting the fluorescent light emitting tube 20 needs to be applied for an extended period of time. Thus, the glow discharge time period, immediately after the fluorescent light emitting tube 20 is started, is also relatively long. As a result, the electron radiating substance filling the electrode filament coils 21 and 22 scatters more violently than in a circuit adopting the usual hot cathode starting system, and therefore there is an undesirable possibility of reducing the lamp life lighting on/off characteristic.
In the structure shown in FIG. 5B including the diodes 28 and 29 connected parallel to the electrode filament coils 21 and 22 and the structure shown in FIG. 5C including the capacitors 31 and 32 connected parallel to the electrode filament coils 21 and 22, the effect of reducing the power loss is relatively small. Moreover, a sufficient number of thermoelectrons are not emitted since a sufficient amount of pre-heating electric current does not flow to the electrode filament coils 21 and 22 before the fluorescent light emitting tube 20 is started. As a result, a larger amount of electron radiating substance scatters, which involves an undesirable possibility of not increasing the lamp life lighting on/off characteristic.
In the structure shown in FIG. 6, a sufficient amount of pre-heating electric current can flow to the electrode filament coils 21 and 22 before an electric current for starting the fluorescent light emitting tube 20 flows, which significantly increases the lamp life lighting on/off characteristic. However, the power loss caused by the heat generation in the electrode filament coils 21 and 22 during the constant light state of the fluorescent light emitting tube 20 is not reduced. The power loss is almost the same as that in the conventional electronic lighting circuit 19 shown in FIG. 4.
A fluorescent lamp lighting apparatus according to the present invention includes a fluorescent light emitting tube; and an electronic lighting circuit for applying an electric current to the fluorescent light emitting tube. The electronic lighting circuit includes a pair of electrode filaments provided in the fluorescent light emitting tube, a pair of capacitor each connected in series to a respective one of the pair of electrode filaments and connected parallel to the fluorescent light emitting tube, and an inductor connected in series to one of the pair of electrode filaments.
In one embodiment of the invention, the electronic lighting circuit further includes a temperature positive characteristic resistance element connected parallel to the pair of capacitors.
In one embodiment of the invention, the electronic lighting circuit further includes an inverter circuit section for applying an electric current for lighting up the fluorescent light emitting tube.
According to the present invention, the electronic lighting circuit includes an inductor connected in series to a fluorescent light emitting tube and a pair of capacitors each connected parallel to the fluorescent light emitting tube. The inductor and the pair of capacitors form a resonating circuit. In such a resonating circuit, the pair of capacitors can be considered as one parallel synthesis capacitor which is connected in series to the fluorescent light emitting tube. A resistance of a pair of electrode filament coils provided in the fluorescent light emitting tube can be considered as one resistance, obtained as a result of synthesizing two parallel resistances, which is connected in series to the resonating circuit.
Since the resistance of the pair of electrode filament coils is considered as one resistance obtained as a result of synthesizing two parallel resistances, the resistance impedance which contributes to the resistance of the pair of electrode filament coils is reduced. Accordingly, the fluorescent light emitting tube is started rapidly, and thus the lamp life lighting on/off characteristic of the fluorescent light emitting tube is improved. In the constant lighting state after the fluorescent light emitting tube is started, the electric current which unnecessarily heats the electrode filament coils is divided into two, and thus the value of the electric current in each electrode filament coil is reduced. As a result, the power loss caused by the heat generation in the electrode filament coils is reduced.
The lamp life lighting on/off characteristic is further improved by providing the temperature positive characteristic resistance element which is connected parallel to the pair of capacitors so that the temperature positive characteristic resistance element is opposite to a power supply, for applying an electric current to the fluorescent light emitting tube, with respect to the fluorescent light emitting tube.
Thus, the invention described herein makes possible the advantages of providing a fluorescent lamp lighting apparatus for reducing a power loss caused by heat generation in an electrode filament coil during a constant lighting state of a fluorescent light emitting lamp and also increasing the lamp life lighting on/off characteristic of the fluorescent light emitting lamp.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.